Method for selective hydrogenation of polyunsaturated compounds into monounsaturated compounds using a homogeneous catalyst

ABSTRACT

A process for the selective hydrogenation of diolefinic compounds to mono-olefinic compounds uses a catalyst composition comprising at least one salt of a transition metal from groups IB, IIB, VB, VIB, VIIB and VIII of the periodic table, at least one ligand and at least one organometallic reducing agent, optionally in the presence of a non-aqueous ionic liquid selected from the group formed by liquid salts with general formula Q + A −  (in which Q +  represents a quaternary ammonium and/or quaternary phosphonium and A −  represents any anion which can form a liquid salt below 90° C.).

The present invention relates to hydrogenating diolefinic compounds tomonoolefinic compounds.

It pertains to a process for hydrogenating unsaturated compounds using acatalytic composition.

Hydrocarbon conversion processes such as steam cracking, visbreaking,catalytic cracking and cokefaction are carried out at high temperaturesto allow a large quantity of unsaturated compounds the formation ofwhich is favoured at high temperatures to be formed: acetyleniccompounds (acetylene, propyne, vinyl- and ethyl-acetylene), diolefiniccompounds such as 1,2-propadiene, 1,2-butadiene and 1,3-butadiene,olefinic compounds such as ethylene, propylene, 1-n-butene, 2-n-butenes,isobutene, pentenes and other compounds the boiling point of which is inthe “gasoline” cut range and which may be olefinic or diolefinic. Themost highly unsaturated compounds (acetylenic and diolefinic) are highlyunstable and very readily produce high molecular weight products(oligomers, gums) by polymerization reactions. Such highly unsaturatedcompounds must therefore be eliminated to allow different cuts derivedfrom said processes to be used for chemistry or for olefinpolymerization processes. As an example, the steam cracking C₄ cutcontains a high proportion of 1,3-butadiene which must be eliminatedbefore it can be used in butene polymerization units. Similarly,methylacetylene (MA) and propadiene (PD) compounds present in the C₃steam cracking cut in an amount of 3% to 4% by weight must be eliminatedbefore the propylene can be used to synthesize polypropylene.Specifications for highly unsaturated compounds for feeds topolymerization units are very severe given the high sensitivity of newclasses of polymerization catalysts (metallocenes) to such compounds.Specifications regarding the quality of polymers produced also requirethat the treated feeds should be very pure.

Conventionally, 1,3-butadiene is separated from the olefinic cut, forexample by extractive distillation in the presence of dimethylformamideor N-methyl-pyrrolidone. The olefinic cut obtained contains isobutane,isobutene, 1-butene, 2-butenes, n-butane and 1,3-butadiene, this latterbeing in an amount of between 0.1% and 2% by weight.

If 1,3-butadiene is not upgraded, the cut can be treated directly over acatalyst in the presence of hydrogen to transform the 1,3-butadiene inton-butenes.

If 2-butene is desired, processes which can produce a great deal of2-butene and separate different compounds must be used, such asselective hydrogenation of 1,3-butadiene to butanes with a high degreeof isomerization of 1-butene to 2-butene. 2-butene is used as afeedstock for petrochemicals. That type of use necessitates almostcomplete hydrogenation of the 1,3-butadiene as its presence can only betolerated in amounts of less than 10 ppm by weight.

When low 1,3-butadiene contents are to be achieved with conventionalnickel or palladium based catalysts, a reduction in the 2-butene contentis observed due to the formation of butane. Limiting consecutivehydrogenation and thus butane formation imposes more restrictions on anysolutions which may be proposed.

A further application that can be envisaged is the reduction in the1,3-butadiene content in a 1-butene rich cut without transforming thelatter into butane or isomerizing it to 2-butene, cis and/or trans. Thatreaction can be integrated into a 1-butene production process carriedout in a finishing reactor which can reduce the 1,3-butadiene content toless than 10 ppm.

As described in the literature (see, for example, “Proceedings of theDGMK conference”, 11-13 Nov. 1993, Kassel, Germany: “Selectivehydrogenation catalysts and processes: bench to industrialscale”—Boitiaux J P et al), the hydrogenation selectivity of highlyunsaturated compounds (diolefins or acetylenic compounds) to olefinsderives from strong complexation of the unsaturated compound on thepalladium, preventing access of the olefins to the catalyst and thuspreventing their transformation into paraffins. This fact is clearlyillustrated in the publication cited above in which 1-butyne isselectively transformed into 1-butene on a palladium-based catalyst.However, it should be noted that this hydrogenation rate is relativelylow, and the kinetics are generally negative with respect to theacetylenic compound. When all of the acetylenic compound has beencompletely converted, consecutive hydrogenation of 1-butene is carriedout at a much higher rate than hydrogenation of the acetylenic compound.In the case of 1,3-butadiene and for conventional catalysts, the dienehydrogenation rate is generally close to that of the olefin when themolecules are not mixed or hydrogenated consecutively.

That phenomenon poses a certain number of problems as regards industrialunits. Firstly, to satisfy specifications for 1,3-butadiene in theolefinic cut, very high 1,3-butadiene conversions are required. This hasthe effect of greatly reducing the concentration of 1,3-butadiene in thereactor and in particular at the outlet, to values which are lower thanthose corresponding to covering the catalyst surface completely. Thus,olefinic molecules have access to the active surface and as theirhydrogenation rate is of the same order as that of 1,3-butadiene, theyare consumed. A large quantity of 1,3-butadiene is transformed intobutane. Thus, it would be of great advantage to find a catalyst thatallowed 1,3-butadiene hydrogenation at a rate which was higher than thatof 2-butene hydrogenation, whether those compounds were hydrogenatedalone or as a mixture. Achieving high selectivities and satisfyingsevere specifications for highly unsaturated compounds thus requirescatalysts that result in high ratios between the 1,3-butadienehydrogenation rate constant and that for butenes. A further interestingcatalytic system is constituted by an active site which can minimize thehydrogenation rate of the least unsaturated compound (olefin)independently of the diolefin or acetylene. The importance of such acatalyst is not limited to an increase in its 2-butene selectivity, butit can also allow better control of the hydrogenation process. In theevent that minor local hydrogen distribution problems are encountered,using such a catalyst does not result in a high degree of conversion ofbutenes to butane and will thus reduce problems connected with highexothermicity linked to such poorly controlled hydrogenations, whichaggravate the distribution problems.

Further, with C₄ cuts which have very low boiling points, it is possibleto keep the catalyst in the reaction medium and to recover the effluentsin the gas phase. Continuous injection of the liquid catalyst,representing several ppm of metal, can be envisaged to keep thecatalytic activity stable over time.

To solve this problem, then, it is of interest to develop ahydrogenation catalyst which would allow hydrogenation of 1,3-butadieneto butenes and which would have low activity for consecutivehydrogenation of 1-butene or 2-butene to butane.

Thus, the aim of the invention is to provide a liquid catalyticcomposition which allows selective hydrogenation of polyunsaturatedcompounds to monounsaturated compounds.

Said catalytic composition allows hydrogenation of diolefinic compoundsto mono-olefinic compounds at rates which are at least 3 times andgenerally about 5 times higher than the hydrogenation rate of α-olefiniccompounds to saturated compounds. This soluble catalyst can be generallydefined as comprising at least one salt of a transition metal fromgroups IB, IIB, VB, VIB, VIIB and VIII, at least one ligand and at leastone organometallic reducing agent.

More particularly, the catalytic composition used in the process of theinvention is characterized:

-   -   in that the metal is at least one metal selected from metals        from groups IB, IIB, VB, VIB, VIIB and VIII, preferably IB, IIB,        VIB and VIII of the periodic table, more particularly from iron,        cobalt, nickel, copper, chromium, molybdenum, zinc, palladium        and ruthenium. Said metals can be introduced in the form of        halides or acetylacetonates, and preferably in the form of        organic acid carboxylates containing 2 to 25 carbon atoms.        Examples of the latter which can be cited are acetates,        octoates, decanoates, naphthenates, stearates, palmitates,        oleates and benzoates;    -   in that the reducing agent is selected from organometallic        derivatives of at least one metal from the group formed by        lithium, sodium, aluminium and even mixed derivatives of        aluminium and sodium and/or lithium. They have at least one        carbon-metal or hydrogen-metal bond, each of said bonds        corresponding to a reducing function. Said reducing agents are        either directly in the liquid form or in the form of a solid        which must be dissolved in a suitable solvent. Examples are        organoaluminic compounds with general formula AlR_(y)(X)_(3-y),        in which R is an alkyl group, for example methyl, ethyl,        isopropyl, butyl, isobutyl or terbutyl, etc; in which X is a        halide and y=1, 2 or 3, magnesians with formula MgR₂,        aluminoxanes, sodium borohydride and various alkaline hydrides        such as LiAlH₄ or NaAlH₄ themselves or their derivatives        obtained by substituting 1 to 3 hydrogen atoms with 1, 2 or 3        alkoxy groups, for example LiAlH₃(OR), LiAlH₂(OR)₂ or LiAlH(OR)₃        in which R is an alkyl group, for example methyl, ethyl,        isopropyl, butyl, isobutyl or tert-butyl; and    -   in that the ligand is selected from derivatives of phosphorus,        arsenic or antimony, or nitrogen-containing ligands.

Examples of ligands selected from phosphorus, arsenic and antimony thatcan be cited are ligands of the following type:YR_(m)X_(3-m), YR₃, R₂Y—(CH₂)_(n)YR₂, Y(OR)₃ or YOR₃,in which Y=P, As or Sb, m=0, 1, 2 or 3; R=alkyl, aryl or substitutedaryl; X=halogen and n=0, 1, 2, 3 or 4.

Examples of nitrogen-containing ligands which can be cited are aminesand polyamines, imidazole, substituted imidazoles, pyrrole andsubstituted pyrroles, pyrazoles, amide derivatives, imines or diimines(produced, for example, by reacting glyoxal with a derivative of anilinesubstituted on the aromatic ring), and finally pyridine derivatives.

Particular examples of ligands have the following general formulae:R—N═CR′—CR′═N—R, PR₃ or R₂P—(CH₂)_(n)—PR₂in which R′=H or CH₃, n=1, 2 or 3 or 4 and R=alkyl, aryl or arylpartially substituted with 1, 2, 3 or 4 methyl, ethyl, isopropyl ormethoxy groups. The following developed formulae illustrate certain ofsaid products:

-   -   2,3-bis(2,6-dimethylphenylimino)butane:

-   -   bis(2,6-dimethylphenylimino)ethane:

-   -   2,3-bis(2-methylphenylimino)butane

-   -   2,3-bis(2,6-diisopropylphenylimino)butane

-   -   2,2-bipyridyl

-   -   2,3-bis(4-methoxyphenylimino)butane:

-   -   diphenylphosphinoethane:

The ligands can also carry a function such as ammonium, phosphonium, acarboxylic acid, an amine, an alcohol or a sulphonate.

Optionally, an organic compound can be used to act as a solvent; thefollowing can act as solvents: aliphatic or aromatic hydrocarbons,ethers, esters, halogenated hydrocarbons and, at low concentrations,sulphoxides and amides; the reaction can also be carried out in theabsence of an additional solvent; it is then the polyunsaturated ormonounsaturated compound which acts as a solvent.

At least one salt of another transition metal selected (for example ifthe principal metal is a metal from group VIII) from metals from groupsIB, VB, VIB, VIIB and VIII, more particularly (for example if theprincipal metal is iron) from Co, Ni, Cu, Rh, Pd, Mn, Mo, W and V,preferably from Ni, Cu, Rh and Pd, can be added to the hydrogenationcatalyst. The additional metal is introduced in a minor proportion withrespect to the principal metal.

It is also possible to carry out the reaction using ionic liquids assolvents for the catalyst.

The invention also concerns a catalytic composition comprising at leastone compound of a transition metal from groups IB, IIB, VB, VIB, VIIBand VIII, at least one ligand, at least one reducing agent and at leastone ionic liquid with formula Q⁺A⁻, as defined below.

Said solvents which are constituted solely by ions, havephysico-chemical properties, in particular their solubility with organiccompounds, which can be modified as a function of the choice of anionand cation. Their application in catalysis has been reviewed severaltimes; the most recent is that by R Sheldon, Chem. Commun 2001, 2399. Itis then possible to select the ionic liquid so that the products fromthe reaction are less miscible in the ionic liquid in which the catalystis dissolved. The reaction thus carried out in a two-phase medium. Theproducts can readily be separated from the catalyst and solvent bysimple decanting. The catalyst and the solvent can be recycled.

The Assignee's U.S. Pat. No. 6,040,263 describes the use of said mediumassociated with complexes of transition metals from groups 8, 9 and 10(or group VIII) for the hydrogenation of unsaturated compounds.

It has been discovered that complexes of transition metals from groupsIB, IIB, VB, VIB, VIIB and VIII, preferably iron, associated with aligand, in an ionic liquid with general formula Q⁺A⁻, are capable ofhydrogenating unsaturated derivatives, in particular diolefins withimproved selectivities and activities. In this case, the ligand ispreferably a nitrogen-containing ligand selected, for example, fromthose described above.

The non-aqueous ionic liquid is selected from the group formed by liquidsalts with general formula Q⁺A⁻ in which Q⁺ represents a quaternaryammonium and/or quaternary phosphonium ion and A⁻ represents any anionwhich is capable of forming a liquid salt at low temperatures, i.e.below 90° C. and advantageously at most 85° C., preferably below 50° C.Preferred anions A⁻ are chloroaluminate ions of the R_(x)Al_(y)X_(z) ⁻type (x=0-4, y=1-3, z=0-10), the nitrate, sulphate, phosphate, acetate,halogenoacetate, tetrafluorborate, tetrachloroborate,hexafluorophosphate, hexafluoroantimonate, fluorosulphonate,alkylsulphonates, perfluoroalkylsulphonates,bis(perfluoroalkylsulphonyl)amides and arenesulphonates, the latteroptionally being substituted with halogen groups or halogenoalkylgroups.

The quaternary ammonium and/or phosphonium ions Q⁺ preferably havegeneral formulae NR¹R²R³R⁴⁺ and PR¹R²R³R⁴⁺ or general formulaeR¹R²N═CR³R⁴⁺ and R¹R²P═CR³R⁴⁺ in which R¹, R², R³ and R⁴, which may beidentical or different, represent hydrogen (with the exception of thecation NH₄ ⁺ for NR¹R²R³R⁴⁺); preferably, a single substituentrepresents hydrogen or hydrocarbyl residues containing 1 to 30 carbonatoms, for example alkyl groups, saturated or non saturated groupscycloalkyl or aromatic groups, aryl or aralkyl groups, which may besubstituted, containing 1 to 30 carbon atoms.

The ammonium and/or phosphonium ion can also be derived fromnitrogen-containing and/or phosphorus-containing heterocycles comprising1, 2 or 3 nitrogen and/or phosphorus atoms, with general formulae:

in which the cycles are constituted by 4 to 10 atoms, preferably 5 to 6atoms, R¹ and R² being as defined above.

The quaternary ammonium or phosphonium can also be a cation withformula:R¹R²⁺N═CR³—R⁵—R³C═N⁺R¹R² orR¹R²⁺P═CR³—R⁵—R³C═P⁺R¹R²in which R¹, R² and R³, which may be identical or different, are definedas above and R⁵ represents an alkylene or phenylene residue. Particulargroups R¹, R², R³ and R⁴ which can be mentioned are methyl, ethyl,propyl, isopropyl, butyl, secondary butyl, tertiary butyl, amyl,methylene, ethylidene, phenyl or benzyl radicals; R⁵ may be a methylene,ethylene, propylene or phenylene group.

The ammonium and/or phosphonium cation Q⁺ is preferably selected fromthe group formed by N-butylpyridinium, N-ethylpyridinium, pyridinium,3-ethyl-1-methylimidazolium, 3-butyl-1-methylimidazolium,3-hexyl-1-methylimidazolium, 3-butyl-1,2-dimethylimidazolium,diethylpyrazolium, N-butyl-N-methylpyrrolidinium,trimethylphenylammonium, tetrabutylphosphonium andtributyl-tetradecylphosphonium.

Examples of salts which can be used in the invention that can be citedare N-butylpyridinium hexafluorophosphate, N-ethylpyridiniumtetrafluoroborate, pyridinium fluorosulphonate,3-butyl-1-methylimidazolium tetrafluoroborate,3-butyl-1-methylimidazolium hexafluoroantimonate,3-butyl-1-methylimidazolium hexafluorophosphate, 3-butyl-1-methylimidazolium trifluoroacetate, 3-butyl-1-methylimidazoliumtrifluoromethylsulphonate, 3-butyl-1-methylimidazoliumbis(trifluoromethylsulphonyl)amide, trimethylphenylammoniumhexafluorophosphate and tetrabutylphosphonium tetrafluoroborate. Thesesalts can be used alone or as a mixture.

The mole ratio between the ligand and the transition metal salt is inthe range 0.5/1 to 10/1, preferably in the range 0.5/1 to 3/1.

If the ligand is monocoordinating, it can usefully be used in aligand/transition metal salt mole ratio of 2/1 to 3/1. If the ligand isbicoordinating, it is preferably used with a ligand/transition metalsalt mole ratio of 1/1 to 1.5/1.

The mole ratio between the reducing agent and the transition metal saltis generally 1/1 to 5/1, preferably 1.2/1 to 5/1.

In accordance with the present invention, the catalyst can be preparedin two ways.

The first consists of separately injecting the products into a stainlesssteel Grignard reactor containing the substrate to be hydrogenated.

The second consists of preparing the mixture ex situ. This procedure hasthe advantage of allowing the possibility of monitoring the reductionstate of the iron visually. When TEA is injected into the flaskcontaining the iron-diimine complex, it can be seen that the initiallyred solution becomes dark brown. A release of gas constituted by anethane/ethylene mixture results from the reducing action of TEA.Further, only a single injection per syringe is required into thecatalysis reactor. The performances obtained in both operating modes arealmost identical.

In general, it is preferable to add the ligand to the iron compound inthe presence of a diolefin, before adding the reducing agent. It is alsopossible to isolate a FeHXL2 (where L is an imine) or FeHXL′ (where L′is a diimine) reduced iron complex in which X is a halogen, anacetylacetonate or a carboxylate and to add an alkylaluminium or anyother reducing agent in the presence of a diolefin.

In the case of selective hydrogenation of 1,3-butadiene, the catalyticcomposition is added to the system in catalytic quantities. Thisquantity, expressed in ppm (parts per million) of metallic compounds inthe reaction medium, is in the range 10 to 10000 ppm, preferably in therange 40 to 300 ppm.

The reaction temperature is in the range 0° C. to 70° C., preferably inthe range 10° C. to 30° C.

The partial pressure of hydrogen is in the range 0 to 20 MPa, preferablyin the range 0.01 to 5 MPa and more preferably in the range 0.5 to 1.5MPa.

The following examples illustrate the invention without limiting itsscope.

EXAMPLE 1

Synthesis of Catalyst

The catalyst defined in the invention was obtained after mixing thethree compounds in the following order: metal salt-ligand-reducingagent, in a mole ratio of 1/1/3 respectively.

a) Preparing a solution of iron salt in n-heptane from iron octoate,which is a viscous brown liquid constituted by iron^(III)2-ethylhexanoate in the presence of a slight excess of 2-ethylhexanoicacid in solution in dearomatized white spirit. That product titrated at10% by weight of iron. A solution in n-heptane was prepared with aconcentration of 0.7 g of iron/100 ml, i.e. 12.5 mMol/100 ml.

b) Preparation of diimine solution (ligand).2,3-bis(2,6-dimethylphenylimino)butane, with the developed formula (1)shown in the paragraph describing the ligands was used. This diimine wasdissolved in n-heptane at a concentration of 1.48 g/100 ml, i.eequivalent to 5 mMol/100 ml.

c) Preparation of solution of reducing agent. Triethylaluminium([Al(Et)₃] or TEA) is liquid in the pure state, and is highly sensitiveto water and to oxygen in the air. This self-ignition faculty in contactwith air disappears when it is in solution diluted in an inert solventsuch as n-paraffins. A dilute solution of triethylaluminium in heptanetitrating 1.32 mMol/ml was used. It should be noted that the heptaneused as the solvent to dissolve the reagents had to be dried in advanceand stored over a molecular sieve to keep it anhydrous.

The first test consisted of introducing in succession, using a syringe,into the Grignard reactor with gentle stirring containing a mixtureconstituted by 120 ml of n-heptane and 8.4 g of 1,3-butadiene maintainedat a temperature of 17° C., 2.7 ml of the iron salt solution, then 6.7ml of the diimine solution and finally 0.8 ml of the TEA solution. Thiscatalytic composition corresponds to an iron composition of the order of200 ppm with respect to the reaction medium.

The Grignard reactor was then placed under 1 Mpa of hydrogen andstirring was increased to increase the solubility of hydrogen in theliquid phase. The hydrogen pressure was kept constant in the Grignardreactor and the hydrogen consumption was measured by the reduction inhydrogen pressure contained in an intermediate trap of known volume.

This mode of operation allowed an estimation with a certain degree ofaccuracy to be made of the theoretical quantity of hydrogen necessary toconvert all of the 1,3-butadiene employed and thus of being able to stopthe reaction and/or take intermediate samples for analysis. Under thetest conditions, hydrogenation of 8.4 g of 1,3-butadiene corresponded toa rapid reduction in pressure in the trap of 3 MPa of hydrogen. Ifhydrogenation was continued, the reaction rate corresponding to theconversion of butenes into butane was accompanied by a substantialreduction in hydrogen consumption.

In the examples given with 1,3-butadiene, a sample was taken assuming atheoretical consumption of 80% 1,3-butadiene conversion. In the presentexample, this conversion was obtained after 94 seconds of reaction.

The performances of the catalytic system (activity, selectivity forcis-2-butene and selectivity for 1-butene) are shown in Table 4.

EXAMPLE 2

The operating procedure of Example 1 was used, except that the catalystwas prepared outside the reactor and injected after ex situ reduction.Identical results were obtained as regards selectivity. The reactiontime to reach 80% 1,3-butadiene conversion was increased by 20 seconds.

EXAMPLE 3

The operating procedure of Example 1 was used, except that half as muchcatalyst was introduced, i.e the equivalent of 100 ppm of iron insteadof 200 ppm. At this catalyst concentration, 80% conversion was obtainedin 120 seconds.

The performances of the catalytic system (activity, selectivity forcis-2-butene and selectivity for 1-butene) are shown in Table 4.

EXAMPLE 4

The operating procedure of Example 1 was used, except that an equivalentof 80 ppm of iron was introduced instead of the 200 ppm and 100 ppm ofExamples 1 and 3. In this example, 80% conversion was obtained in 188seconds. This value was obtained using a hydrogen consumption curve; thevalues shown in Table 1 allowed several points to be traced.

The performances of the catalytic system (activity, selectivity forcis-2-butene and selectivity for 1-butene) are shown in Table 4.

TABLE 1 1,3- selectivity time n-C4 trans 2-bu 1-bu cis 2-bu butadienecis-2-bu /Σ (sec) (%) (%) (%) (%) (%) butenes 105 0.15 0.10 040 60.9538.35 99.18 162 0.20 0.20 0.55 75.85 23.20 99.02 488 0.40 0.30 0.9597.85 0.55 98.74

EXAMPLE 5 Comparative Example Using the Catalytic System of theInvention without Using a Ligand

An iron concentration of 200 ppm was used, as in Example 1, with anAlEt₃/Fe ratio of 3.

80% conversion to 1,3-butadiene was obtained after 125 seconds and thecomposition of the reaction medium is shown in Table 2.

TABLE 2 1,3- selectivity time n-C4 trans 2-bu 1-bu cis 2-bu butadienecis-2-bu /Σ (sec) (%) (%) (%) (%) (%) butenes 35 0.95 1.40 9.20 10.4578.00 49.64 118 3.65 5.65 34.75 26.75 29.20 39.84 140 5.45 7.60 44.8030.65 11.50 36.90 154 17.65 9.90 45.95 31.95 0.55 36.39

EXAMPLE 6

The procedure of Example 1 was repeated, replacing the ligand[2,3-bis(2,6-dimethylphenylimino)butane] with[2,3-bis(2,6-diisopropylphenylimino)butane] (see developed formula n^(o)4). The reaction time to achieve 80% 1,3-butadiene conversion was 22seconds.

The results are shown in Table 3

TABLE 3 1,3- selectivity time n-C4 trans 2-bu 1-bu cis 2-bu butadienecis-2-bu /Σ (sec) (%) (%) (%) (%) (%) butenes 15 0.15 0.05 0.10 56.6043.10 99.70 20 0.15 0.10 0.15 71.70 27.90 99.67 30 0.15 0.10 0.20 98.201.35 99.71 102 2.50 3.35 0.60 93.15 0.40 95.89

EXAMPLE 7 Comparative Test Between the Catalyst of the Invention and aHeterogeneous Catalyst Constituted by Palladium Supported on AluminaUnder the Operating Conditions Used in Example 1

2 g of palladium/alumina catalyst containing 0.3% of Pd was introducedinto the Grignard reactor. Table 6 compares the catalytic activity,expressed in moles of 1,3-butadiene consumed/minutes/g of metal.

The selectivity for cis 2-butene and 1-butene were also compared. Theseselectivities were measured for a 1,3-butadiene conversion of 80%.

The results are shown in Table 4.

TABLE 4 activity selectivity* (mol/min/g of for cis selectivity* forexample catalyst metal) 2-butene (%) 1-butene (%) 1 iron (200 ppm) 4.7498.50 1 3 iron (100 ppm) 2.88 99.01 0.8 4 iron (80 ppm) 2.23 98.60 1 7Pd/Al₂O₃ 1.98 20.00 60 *selectivities measured at 80% 1,3-butadieneconversion.

The catalyst, which was conventionally used in heterogeneous catalyst,could not directly produce cis 2-butene, but mainly 1-butene.

The compared activity, expressed in moles of converted 1,3-butadiene perminute and per gram of metal, was up to 2.4 times higher with thehomogeneous iron-based catalyst. Further, the cis 2-butene selectivitywas very high: close to 99%.

The particular feature of the catalytic system was simply the very smallquantity of 1-butene produced, for example for example 3 the very smallquantity of n-butane formed with a remaining quantity of 1,3-butadieneof the order of 0.5%.

EXAMPLE 8

The operating procedure of Example 1 was used, but the composition ofthe substrate to be hydrogenated was different. It was a mixturecomposed of 50% of 1,3-butadiene and 50% of 1-butene.

TABLE 5 1,3- 1,3- butadiene time n-C4 trans 2-bu 1-bu cis 2-bu butadieneconversion (sec) (%) (%) (%) (%) (%) (%) 72 0.16 0.00 50.50 21.03 25.4049.20 288 0.14 0.00 50.57 42.80 3.58 92.95 498 0.50 0.35 50.24 45.940.00 100.00

It should also be noted that the catalytic system completely transformedthe 1,3-butadiene principally to cis 2-butene without touching the1-butene molecule which could produce cis or trans 2-butene byisomerization or n-butane after hydrogenation.

EXAMPLE 9

The catalytic system used in Example 1 was used, but the nature of thefeed to be hydrogenated was replaced with 2,4-hexadiene.

The catalysis temperature was 22° C. and the hydrogen pressure was 1MPa.

The concentration of iron in the reaction medium was 200 ppm and thereaction time to reach 80% 1,3-butadiene conversion was 60 seconds.

The results are shown in Table 6.

TABLE 6 trans 2- 1- cis 2- 2,4- selectivity time n-C6 hexane hexanehexane hexadiene t-2 hex/Σ (sec) (%) (%) (%) (%) (%) hexenes 45 0.4063.25 0.15 0.70 35.45 98.67 60 0.35 79.40 0.20 0.95 19.15 98.57 80 0.5086.70 0.20 1.10 11.50 98.52 95 0.45 93.10 0.20 1.50 4.80 98.21 110 0.8596.85 0.20 2.05 0.10 97.73

1. A process for the selective hydrogenation of 1,3-butadiene containedin a feed, comprising the passage of a feed containing 1,3-butadiene incontact with a liquid catalyst composition, characterized in that saidliquid catalyst composition comprises at least one salt of a transitionmetal from groups IB, IIB, VB, VIB, VIIB and VIII of the periodic table,at least one ligand and at least one organometallic reducing agent, saidcontact resulting in a conversion of said 1,3-butadiene to primarilycis-2-butene.
 2. A process according to claim 1, characterized in that:the transition metal salt is selected from halides, acetylacetonates andcarboxylates of organic acids containing 2 to 25 carbon atoms; thereducing agent is selected from organometallic derivatives of at leastone metal selected from the group formed by lithium, sodium andaluminium; the ligand is selected from derivatives of phosphorus,arsenic and antimony and nitrogen-containing ligands.
 3. A processaccording to claim 2, wherein the transistion metal salt is carboxylateselected from acetates, octoates, decanoates, naphthenates, stearates,palmitates, oleates and benzoates.
 4. A process according to claim 1,characterized in that the transition metal salt is selected from saltsof metals from groups IB, IIB, VIB and VIII of the periodic table.
 5. Aprocess according to claim 4, characterized in that the transition metalsalt is selected from copper, zinc, chromium, molybdenum, iron, cobalt,nickel, ruthenium and palladium salts.
 6. A process according to claim5, characterized in that the transition metal salt is selected from ironsalts.
 7. A process according to claim 1, characterized in that thereducing agent is selected from: organoaluminas with general formulaAlR_(y)(X)_(3-y), in which R is an alkyl group, X is a halide and y=1, 2or 3; magnesias with formula MgR₂, in which R is as defined above;aluminoxanes; sodium borohydride; and alkaline hydrides and theirsubstitution derivatives comprising 1, 2 or 3 alkoxy groups.
 8. Aprocess according to claim 1, characterized in that the ligand derivedfrom phosphorus, arsenic or antimony is selected from ligands withgeneral formulae:YR_(m)X_(3-m), YR₃, R₂Y—(CH₂)_(n)YR₂, Y(OR)₃ and YOR₃, in which Y=P, Asor Sb, m=0, 1, 2 or 3; R=alkyl, aryl or substituted aryl; X=halogen, andn=0, 1, 2, 3 or
 4. 9. A process according to claim 1, characterized inthat the nitrogen-containing ligand is selected from amines, polyamines,imidazole, substituted imidazoles, pyrrole, substituted pyrroles,pyrazoles, amide derivatives, imines, diimines and pyridine derivatives.10. A process according to claim 1 characterized in that a minorproportion of at least one salt of a further transition metal selectedfrom metals from groups IB, VB, VIB, VIIB and VIII is added to thecatalyst.
 11. A process according to claim 10, characterized in that theprincipal metal is iron and the additional metal is selected from Co,Ni, Cu, Rh, Pd, Mn, Mo, W and V.
 12. A process according to claim 1,characterized in that the catalyst composition is dissolved in at leastone organic compound selected from aliphatic or aromatic hydrocarbons,ethers, esters, halogenated hydrocarbons, sulphoxides and amides.
 13. Aprocess according to claim 1, characterized in that the catalystcomposition is dissolved in at least one ionic liquid with generalformula Q⁺A⁻ in which Q⁺ represents a quaternary ammonium and/orquaternary phosphonium ion and A³¹ represents any anion which is capableof forming a liquid salt at low temperatures, i.e. below 90° C.
 14. Aprocess according to claim 13, characterized in that the quaternaryammonium and/or phosphonium ion Q⁺ has one of the following generalformulae:NR¹R²R³R⁴⁺ and PR¹R²R³R⁴⁺ or one of general formulae:R¹R²N═CR³R⁴⁺ and R¹R²P═CR³R⁴⁺ in which R¹, R², R³ and R⁴, which may beidentical or different, each represent hydrogen, the cation NH₄ ⁺ beingexcluded for NR¹R²R³R⁴⁺, or a hydrocarbyl residue containing 1 to 30carbon atoms.
 15. A process according to claim 13, characterized in thatthe quaternary ammonium and/or phosphonium ion Q⁺ derives from anitrogen-containing or phosphorus-containing heterocycle comprising 1, 2or 3 nitrogen or phosphorus atoms, having one of the following generalformulae:

in which the cycles are constituted by 4 to 10 atoms and R¹ and R²,which may be identical or different, each represent hydrogen or ahydrocarbyl residue containing 1 to 30 carbon atoms.
 16. A processaccording to claim 13, characterized in that the quaternary ammoniumand/or phosphonium ion has one of the following formulae:R¹R²⁺N═CR³—R⁵—R³C═N⁺R¹R² orR¹R²⁺P═CR³—R⁵—R³C═P⁺R¹R² in which R¹, R² and R³, which may be identicalor different, each represent hydrogen or a hydrocarbyl residuecontaining 1 to 30 carbon atoms and R⁵ an alkylene or phenylene residue.17. A process according to claim 1, characterized in that the mole ratiobetween the ligand and the transition metal salt is in the range 0.5/1to 10/1.
 18. A process according to claim 1, characterized in that theligand is monocoordinating and the ligand/transition metal salt moleratio is 2/1 to 3/1.
 19. A process according to claim 1, characterizedin that the ligand is bi-coordinating and the ligand/transition metalsalt mole ratio is 1/1 to 1.5/1.
 20. A process according to claim 1,characterized in that the mole ratio between the reducing agent and thetransition metal salt is 1/1 to 15/1.
 21. A process according to claim1, characterized in that said catalyst composition is employed in aproportion corresponding to a proportion of metallic compounds in thereaction medium of 10 to 10000 ppm by weight.
 22. An integrated processfor producing 1-butene from a 1-butene rich C₄ cut, characterized inthat it comprises, as the finishing step, selective hydrogenation of1,3-butadiene carried out using a process according to claim 1 to obtaina 1,3-butadiene content of less than 10 ppm by weight.
 23. A processaccording to claim 1 conducted under conditions resulting in aselectivity of cis-2-butene of over 98% for an 80% 1,3-butadieneconversion.
 24. A process according to claim 23 wherein the catalystcomprises an iron salt and the ligand is an imino compound.